This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. I am interested in studying how the genetic structure of invasive plant populations affect the ecology of those populations. I want to address this question at two different scales;between-species interactions and within-species interactions. To study how hybridization affects between-species interactions I will utilize two closely related species of thistles (Cirsium altissimum and Cirsium vulgare) and examine the potential for hybridization. If I find hybrids, I eventually plan to compare the performance, growth and reproduction, of the hybrids compared to the parent species. To study within-species interactions, I will examine the genetic structure of Canada thistle (Cirsium arvense) populations to determine of population growth is due to sexual or asexual reproduction. This can have important implications for the management of this noxious weed, as it would allow us to focus control efforts on the appropriate life stage.